1. Field of the Invention
The present invention relates to roller reamers and stabilizers used in the earth drilling industry and, more particularly, to a novel system and method for mounting reamer cutters onto the body of the reamer.
2. The Prior Art
When drilling deep bore holes for oil wells or the like, it is usually necessary to include one or more reamers in the drill string to maintain the proper gauge of the hole and to remove any ledges or obstructions that may block the hole. Such reamers may also be used as stabilizers to prevent changes from occurring in the angle at which the bore hole is drilled. For example, roller reamers which are positioned in the drill string immediately above the drill bit are generally referred to as "bit reamers" or "bottom hole reamers," which are used to maintain the proper gauge of the hole near the bit to minimize the back-to-bottom reaming which would otherwise be necessary when a worn out bit is replaced by a new bit. Roller reamers are placed in the drill string at various points further up the string to provide stabilization by reaming out "dog legs," "key seats," and ledges which may be formed in the bore hole. Stabilization is especially important when drilling directional wells.
In the past, some types of prior art roller reamers have used reamer cutters which are welded into place on the body of the reamer. Since reamer/stabilizers are frequently designed for use in hard rock formations, the reamer cutters eventually become worn and have to be either repaired or replaced. In those types of prior art reamer/stabilizers in which the reamer cutters are welded into place, replacement of the cutters presents a serious problem. Often, the entire reamer must be discarded after the cutter becomes worn. In the alternative, the weld which secures the reamer cutter must be torch-cut so that the assembly can be removed and replaced with a new cutter. This can be a very time consuming and difficult process that requires additional welding equipment along with the services of a skilled welder. This obviously increases the expense and inconvenience involved and is thus not a very desirable alternative.
These problems have led to the development of another type of prior art reamer/stabilizer which has been designed to permit the drilling crew to be able to replace the reamer cutter without having to cut through a weld. This type of prior art reamer is generally illustrated in FIG. 1. As shown in FIG. 1, the reamer/stabilizer has a body 12 which is formed from a length of pipe. The body 12 has a threaded female fitting 14 and a threaded male fitting 16 at opposite ends thereof so that the reamer body can be attached to the other lengths of pipe which form the drill string. In the illustration of FIG. 1, the reamer/stabilizer is provided with three reamer cutters, two of which are shown at 18a, which are equally spaced about the lower portion of the reamer. Three more cutters, two of which are shown at 18b, are equally spaced about the upper portion of the reamer/stabilizer. Each reamer cutter 18 is identical in configuration and in the manner in which they are secured to the body 12 of the reamer/stabilizer.
As best illustrated by the portion of FIG. 1 which is shown in exploded perspective, each reamer cutter 18 has a bore 20 through its center which is designed to receive a bearing pin 22. Bearing blocks 24-25 are placed at the ends of the reamer cutter 18 and each bearing block 24-25 has a corresponding bore 26-27 through which the bearing pin 22 is inserted.
In order to install the reamer cutters 18 on the reamer body 12, the lower bearing block 24 is first placed in the pocket 32 that is cut into the face of the reamer body 12. The bearing block 24 is then pounded with a large sledge hammer so that the slots 28-29 will engage corresponding mill flats 36 which are formed in the lower end 34 of the pocket 32. The upper bearing block 25 is then placed in the pocket 32 and is also pounded with a large sledge hammer until the slots 30-31 of bearing block 25 engage the corresponding mill flats 37 in the upper end 35 of pocket 32. The reamer cutter 18 is then positioned in the pocket 32 between the bearing blocks 24 and 25. Next, the bearing pin 22 is placed in the elongated dressing slot 38 and is then pounded with a sledge hammer until the leading end 21 of bearing pin 22 is fully inserted through the bore 26 of the lower bearing block 24. When the bearing pin 22 is fully inserted through the upper bearing block 25, cutter 18 and lower bearing block 24, the leading end 21 may be grasped and rotated until the small hole 42 at the trailing end of pin 22 is positioned adjacent slot 39. A retaining pin 40 is then inserted through slot 39 and hole 33 using a punch and hammer until it engages the hole 42 at the end of the bearing pin 22. Pin 40 prevents the bearing pin 22 from rotating. Finally, a second retaining pin 44 is inserted behind the upper end of the bearing pin 22 in the dressing slot 38 to prevent the bearing pin 22 from moving longitudinally once it has been properly inserted.
In order to remove and replace the reamer cutter 18, a reverse procedure is followed. That is to say, retaining pin 44 is first removed, pin 40 is then removed using a punch and hammer and then bearing pin 22 is removed by inserting a punch into the lower end 46 of the dressing slot 38 and by pounding the end of the bearing pin 22 until it is removed from the bearing blocks 24-25 and the reamer cutter 18. The reamer cutter 18 is then removed from between the bearing blocks 24 and 25, and then bearing block 25 is pounded with a large sledge hammer so as to disengage the bearing block 25 from the mill flats 37 which retain it. Bearing block 24 is removed in a similar manner.
This type of prior art reamer/stabilizer has a certain advantage in that the bearing blocks and reamer cutter can be more easily replaced than in those types of reamer/stabilizers in which the bearing blocks are welded. However, there are also serious disadvantages with this type of prior art reamer/stabilizer. For example, it is very difficult, particularly in very cold climates, to insert or remove the bearing blocks 24 and 25. A great deal of force is required and frequently the hard hammer blows result in damage to the mill flats 36-37 or corresponding slots 28-31 of the bearing blocks. Since the mill flats 36-37 are used to retain the bearing blocks 24 and 25 in the pocket, damage to the mill flats may result in a situation in which the tremendous centrifugal force exerted by the rapidly rotating drill string will cause the bearing blocks to tear loose from the pocket, resulting in serious damage to equipment and costly down time. Damage can also occur if the retaining pin 44 is lost or broken when drilling.
Another disadvantage with this type of prior art reamer/stabilizer is that the extremely hard hammer blows which are required to insert or remove the bearing pin 22 may shatter the pin because it is typically constructed of an extremely hard, brittle metal. The shattered fragments can oftentimes cause serious injuries to the drilling crew as they attempt to remove or replace a reamer cutter. Thus, special protective equipment such as safety glasses or face shields are required to be worn by drill crews when changing the reamer cutters, and even then serious injuries can sometimes occur.
Yet another disadvantage of this type of prior art reamer/stabilizer is that the elongated dressing slots 38 have a tendency to "whip" the drilling mud as the drill string rotates, thus increasing the strain and torque required to turn the drill string assembly.
In view of the foregoing, it is readily apparent that what is needed in the art is a reamer/stabilizer which effectively overcomes the disadvantages of the prior art type reamer/stabilizers.